1. Field of the Invention
The present invention relates generally to a modulation method of cooperative transmitting point. Example of cooperative transmitting point can be eNB cell, pico, Femto, or RRH.
2. Description of the Related Art
In order to increase the capacity of the modern radio access systems, Cooperative Multipoint (CoMP) transmission and reception has been proposed. Traditionally, in cellular systems each user is assigned to a base station on the basis of criteria such as down link signal strength. At the terminal side, all the signals coming from the other base stations are deemed as interference, which ultimately limit the capacity. In the uplink, the user terminal (UE) only communicates with only one single serving base station while causing interference to the neighboring base station. Also, each base station processes in-cell users independently, and the rest of the users are seen as inter-cell interference.
With CoMP, several geographically distributed base stations cooperate in the transmission and reception with the aim of reducing interference. Cooperation among these base stations are enabled by the high speed link, such as optical fiber links, between them.
For DL-CoMP, multiple base stations in a CoMP set simultaneous transmitting to the same UE. Multiple-input and Multiple output antenna technologies, such as spatial multiplexing or space time block coding, could be employed.
Usually at terminal side, UE is expected to receive multiple data streams from different base station. There are two scenarios. First, when space time blocking coding is employed, as the rank of the data is 1, relatively simple receiver structure is required thus leading to reduced implementation complexity at the UE side. Admittedly, there is a penalty in the aspect of spectrum efficiency.
To achieve higher spectrum efficiency as compare to spatial time blocking coding, open loop spatial multiplexing is employed. In this case, more complex receiver, such as MMSE receiver is needed at UE side, consequently increasing UE implementation complexity.
There is a need to achieve higher spectrum efficiency in the CoMP system, at the same time keeping a relative low terminal implementation cost. This is especially useful for Machine-to-Machine application where the terminal cost is a major issue.